The present invention relates to a photosensitive resin composition, a pattern forming process using said resin composition and electronic devices using the same.
Photosensitive resin compositions may be classified into the polarity changeable type in which the polarity of the exposed portion is changed to produce a difference in solubility and the crosslinked type in which the crosslinking reaction is advanced by exposure to light and the exposed portion is insolubilized. The polarity changeable type can be utilized either as a positive type or as a negative type depending on the developing solution composition, but the crosslinked type is available only as a negative type in principle. The crosslinked type photosensitive material is also disadvantageous in carrying out fine working of high resolution because of the occurrence of swelling of the exposed portion by the developing solution. Further, from the standpoint of prevention of environmental pollution or improvement of working environment, the development of a photosensitive resin composition that can be developed with an aqueous solvent and supersede the conventional photosensitive resin compositions requiring use of a developing solution essentially comprising a chlorine type solvent or an organic solvent has been strongly desired.
Hitherto, polyimide resins having excellent heat resistance have been widely studied for use as an organic photosensitive resin.
For example, it is practiced in the art to coat a polyamide acid, which is a polyimide precursor, on a substrate, subject the coat to a heat treatment to convert polyamide acid and into polyimide, form a photoresist relief pattern on the polyimide film and selectively etch the polyimide with a hydrazine type etching agent to transfer the relief pattern to the polyimide.
However, since polyimide pattern formation in the above process involves the steps for coating of the photoresist and release thereof, the process is very complicated. Also, lowering of dimensional precison may occur due to transfer of the relief pattern through a resist. Thus, in order to realize simplification and higher accuracy of fine working, the development of a heat-resistant substance which is capable of direct fine working with light has been required.
As the materials that can serve the above purpose, there have been proposed various materials such as a photosensitive heat-resistant material composed of a polyamide acid and a bichromate (JP-B-49-17374), a photosensitive polyamide acid derived from a pyromellitic acid derivative (JP-A-49-112241), a photosensitive heat-resistant material composed of a polyamide acid and an unsaturated amine (JP-A-54-145794) and a photosensitive heat-resistant material made by reacting a polyamide acid and a saturated epoxy compound (JP-A-55-45746). However, all of the above-mentioned photosensitive materials are of the negative type prepared by using a crosslinking reaction. The sensitive materials made by applying a crosslinking reaction are disadvantageous in carrying out fine working of high resolution because of the occurrence of swelling of the exposed portion by the developing solution. Also, there are the occasions where a positive type photosensitive heat-resistant material is required from the nature of the process. Thus, a polarity changeable type photosensitive heat-resistant material has been required. As the materials that can serve the above purpose, there have been proposed positive type photosensitive heat-resistant materials (JP-B-1-59571 and JP-A-62-229242).
However, for obtaining said positive type photosensitive heat-resistant material, it has been necessary to use an acid chloride as monomer and to strictly control the working conditions such as reaction temperature, removal of moisture, etc., in the synthesis of said materials. Also, the produced precursor had problems relating to purity, such as the necessity to remove the chlorine ions. Further, since the photosensitive groups in said positive type photosensitive heat-resistant materials are attached to the polyimide precursor by strong covalent linkage, such groups are hard to eliminate in the course of imidization, giving an adverse influence to the produced film properties. The film developing characteristics were also unsatisfactory.